Mildew found my snap peas, because Mother Nature is a hater, and because these things happen when you start greenhouse gardening with hardly two specks of know-how. I did learn something from the loss of our bean plants, so I picked up a spray bottle from the dollar store and got to spraying with an ACV/water solution. I used about 1/2 TBS of vinegar for this spray bottle full of water. Even after dousing the entire greenhouse, I have more than half the bottle left. I can't tell if it's helping yet, but I'll keep trying, since it's as close as I can get to shooting Mildew at point-blank range in the face.
I'm actually feeling frantic, because the mildew that affects beans can also affect tomatoes. I did a bit more reading and stumbled across Growing A Greener World. I'm no longer sure why the rest of the internet still exists, because they have everything: episodes (great news for those of us who have inadvertently become internet-addicted by not owning a television), recipes,blogs, a store, and salvation
from powdery mildew: potassium bicarbonate. It's the only natural treatment for
powdery mildews I've come across that left me any hope it could treat
the mildew that's already there. Potassium bicarbonate is similar to baking soda, but with sodium instead of potassium, it's gentler on plants. And tougher on mildew. Disclaimer so you don't get false hope for Actual Science around here: I'm not so much great at chemistry as highly skilled in google-ing.